Summary The prognostic value of several clinical and histopathological characteristics has been evaluated in patients with Dukes' B and C carcinoma of the rectum and the rectosigmoid. Data on 260 Dukes' B and 208 Dukes' C tumours entered into a prospective, randomized clinical trial of post-operative radiotherapy (5OGy given with 2Gy/fraction in an overall time of 7 weeks) were analyzed by means of the Cox proportional hazards model. The Dukes' stages B and C were analyzed in two separate multivariate analyses. In patients with Dukes' B tumours, a poor prognosis was associated with age above 60, perineural and venous invasion, tumour located 3.2 ng ml-1). In patients with Dukes' C tumours, perineural and venous invasion, tumour located 80 years, non-radical surgery, bedridden more than 50% of day 20-25 days after surgery, post-operative complications, previous cancer within 5 years and previous radiotherapy. A detailed description of material and methods has been published in Balslev et al. (1982Balslev et al. ( , 1986 Table I.